The present invention relates to an operating method for a cooling path for cooling a rolled product, particularly metal, preferably steel. As sections of the rolled product pass through the cooling path, they are initially cooled in a first cooling phase by front cooling devices of the cooling path using a liquid cooling medium. The rolled product sections, are then not cooled using the liquid cooling medium in a second cooling phase which follows the first cooling phase. The rolled product sections are finally cooled again by rear cooling devices of the cooling path using the liquid cooling medium in a third cooling phase which follows the second cooling phase.
A control device of the cooling path in each case receives an initial energy value which is exhibited by the rolled product sections before they pass through the cooling path, and the control device additionally receives a target energy.
On the basis of the initial energy value and the target energy, the control device determines a first target cooling medium profile which is to be applied to the respective section of the rolled product in the first cooling phase, and the control device activates the front cooling devices in accordance with the first target cooling medium profile while the respective section of the rolled product is passing through the front cooling devices.
The present invention further relates to a computer program comprising machine code which can be executed by a control device for a cooling path, wherein the execution of the machine code by the control device causes the control device to operate the cooling path in accordance with such an operating method.
The present invention further relates to a control device for a cooling path, wherein the control device is programmed by such a computer program.
The present invention further relates to a cooling path for cooling a rolled product. The cooling path has front and rear cooling devices, which apply a respective cooling medium quantity to a section of the rolled product that is situated in an active region of the respective cooling device. The cooling path has a transport device, which transports the rolled product through the cooling path, such that the sections of the rolled product pass through the active regions of the cooling devices in succession. A control device operates the cooling path in accordance with such an operating method.
Such an operating method is known from DE 10 2008 011 303 B4 (corresponding to U.S. Pat. No. 8,369,979 B2) and WO 2005/099 923 A1 (corresponding to U.S. Pat. No. 7,853,348 B2), for example. The operating method disclosed in DE 10 2008 011 303 B4, does not disclose in detail the form of the cooling during the third cooling phase.
In the operating method disclosed in WO 2005/099 923 A1, the rolled product is quenched to a target temperature or below in the third cooling phase.
Steel is produced in a hot strip rolling mill or plate rolling mill. Material properties of the rolled product are determined by cooling of the rolled product in the cooling path of the hot strip rolling mill or plate rolling mill. The resulting material properties are also dependent on the time-relative profile of the cooling process.
The time-relative cooling profile is often specified as a time-relative temperature profile. In many cases, a distribution of a water quantity is also specified according to a given cooling strategy combined with a temperature at the end of the cooling path. A two-stage approach is also possible, involving the additional specification of a further temperature at a measuring point within the cooling path. The specification of a temperature is often disadvantageous or problematic, however, due to phase transitions that occur. As a result of the transition heat that occurs during the phase transitions, the specification of cooling based on the temperature is in many cases no longer definite, i.e. there is more than one solution in respect of the water quantity to be applied to the rolled product. However, the material properties resulting from the different solutions then vary.
The operating method disclosed in DE 10 2008 011 303 B4 already works well, even for steels having a high carbon content. However, this method has the disadvantage that the phase transition per se can only be monitored in a suboptimal manner. In particular, it is often not possible to determine the cooling in such a way that the phase transition requires a minimal time. This is disadvantageous in the case of relatively short cooling paths in particular. If the cooling by the air surrounding the rolled product and by the contact with the transport rollers of the cooling path provides a relatively high contribution to the overall cooling, it is also difficult to keep the material properties constant. In the case of relatively long cooling paths, however, it is normal practice to work with an intermediate temperature measurement in the context of a two-stage cooling. In this case, the phase transition can take place relatively quickly. However, this method is limited if the phase transition has already started, since the feedback control is no longer definite if the phase transition is not yet complete at the end of the cooling path.